The invention relates generally to rate gyroscopes and, more particularly, to angular rate optical detection systems for use in such gyroscopes.
As is known in the art, rate gyroscopes have been used in a variety of applications, such as, homing missile systems for the stabilization of a seeker tracking system and for stabilization of the missile through an autopilot.
A gyroscope which, instead of measuring displacement from a reference line, measures the rate-of-change of displacement about a line or axis, (referred to as angular rate) and this device is referred to as a rate gyroscope. One type of rate gyroscope is a single degree of freedom rate gyroscope. Here a mass is adapted to rotate about a spin axis of the gyroscope. A gyroscope rotates or precesses about an axis in quadrature to both the spin vector and the torque vector. The term quadrature refers to the fact that the axis of precession, input axis and spin axis are mutually orthogonal. It follows then that if angular rates are to be measured, three separate, single degree of freedom, rate gyroscopes would be required.
A second type of rate gyroscope is a two degree of freedom rate gyroscope. In this gyroscope the base surface can rotate around two quadrature axes (axes at right angles to each other) such as the inner gimbal and the outer gimbal axis without disturbing the stabilized reference line. One such gyroscope includes a shaft having a precisely machined, flexible end portion. A mass is coupled to the flexible end portion of the shaft. When a torque is applied to the gyro, the spin vector tries to move into the torque vector giving rise to a precession about an axis in quadrature to both the spin and torque vectors. The mass is adapted to pivot about the precession axis in response to angular rates about the spin and torque axes. While such an arrangement is useful in some applications, it is relatively difficult to accurately produce the flexible end portion of the shaft and provide a relatively inexpensive accurate, two degree of freedom rate gyroscope.
Typically, a gyroscope rotates about an axis in quadrature to both the spin and torque vectors. The spin axis, then, is stabilized in space if some kind of angle measuring gadget is provided to convert the mechanical angular orientation of the rotating mass to a corresponding electrical system. Included in the prior art gadgets are potentiometers, synchros, E-pickoffs, and the like, used to measure the rotation of the base surface around the inner gimbal and the outer gimbal axis. With this data we can then determine how far the base surface has moved from a stabilized reference line, for example, the gyro spin axis. The angle measuring gadgets will inform us how far the vehicle has deviated from some predetermined position. These pickoff signals can be used to actuate control circuitry to compensate for undesired movement of the vehicle.